Merge branch 'js/rebase-r-safer-label'

A label used in the todo list that are generated by "git rebase --rebase-merges" is used as a part of a refname; the logic to come up with the label has been tightened to avoid names that cannot be used as such. * js/rebase-r-safer-label: rebase -r: let `label` generate safer labels rebase-merges: move labels' whitespace mangling into `label_oid()`